This invention relates to seismic exploration and more particularly to methods and systems for obtaining and utilizing seismic data obtained from expanding-spreads.
In a more specific aspect of the invention, velocity profiles are now made available for vertical sections of earth formations underlying expanding-spread profiles, which heretofore have been available only by actual measurements in holes drilled through such sections.
In seismic exploration, acoustic waves generated by production of seismic impulses as by explosion of a charge of dynamite or by weight dropping techniques at near surface sending stations are detected after reflection from subsurface beds to produce seismic signals which by reason of time occurrence of reflection components therein are related to the depth and the attitude of subsurface reflecting beds. However, due to the nature of the seismic process itself and the instrumentation employed for detecting and recording such signals, the useful information may be considered to be that from a very narrow band as compared with the seismic waves initially generated. Therefore, the information and data from ordinary seismic records as to the depth and layering of surface structures are correspondingly limited.
In the past, detailed and exact data as to the acoustic properties of the subsurface formations have been obtained by incremental velocity logs of bore holes extending through the formation of interest. However, it frequently is most desirable to be able to obtain such information without the attendant expense of a drilling program to provide the necessary bore holes.